Not Sure If Pregnant?

Mo

So my fiancé and I have sex without a condom quite frequently but he never finishes inside me. I know that it's very rare and unlikely to get pregnant from traces of semen in precum, but I'm already 4 days late and I haven't shown signs that I'm about to get my period. I'm also on birth control (Hormonal IUD) too because I usually have irregular periods. When should I take a pregnancy test?